1. Field of the Invention
The present invention generally relates to heat exchangers comprising tubes that carry a coolant or other heat transfer medium to and from a pair of manifolds, such as those of the type used as evaporators in automobile air-conditioning systems. More particularly, this invention relates a heat exchanger manifold comprising a tank plate and a header plate in which tube ports are formed, and in which ribs are present on the interior of the header plate to define tube stops that positively locate the ends of the tubes within the manifold.
2. Description of the Related Art
Heat exchangers are employed within the automotive industry as condensers and evaporators for use in air conditioning systems, radiators for cooling engine coolant, and heater cores for internal climate control. In order to efficiently maximize the amount of surface area available for transferring heat between the environment and a fluid flowing through the heat exchanger, heat exchanger designs are typically of a tube-and-fin type in which numerous tubes thermally communicate with high surface area fins. The fins enhance the ability of the heat exchanger to transfer heat from the fluid to the environment, or vice versa. For example, heat exchangers used the automotive industry as air conditioner evaporators serve to vaporize a refrigerant by transferring heat from air forced over the external surfaces of the evaporator to the refrigerant flowing through the evaporator.
One type of heat exchanger used in the automotive industry is constructed of a number of parallel tubes that are joined to and between a pair of manifolds, creating a parallel flow arrangement. An internal passage within each manifold defines a reservoir that is in fluidic communication with tubes through tube ports, e.g., holes or slots, formed in the manifold. One or both manifolds include one or more inlet and outlet ports through which a heat transfer fluid enters and exits the heat exchanger. To promote thermal efficiency, such heat exchangers have been constructed by soldering or brazing the tubes to their respective ports. Finally, fins are provided in the form of panels having apertures through which the tubes are inserted, or in the form of sinusoidal centers that can be positioned between adjacent pairs oblong or xe2x80x9cflatxe2x80x9d tubes. A notable flat tube design is known as a microtube, whose oval shape accommodates a row of small parallel passages separated walls (webs) formed integrally with the microtube, such that heat transfer is enhanced by increasing the surface area in contact with the heat transfer fluid.
Various manifold constructions have been suggested. Tubular manifolds with a circular cross-section have typically been preferred for use in high pressure applications, such as evaporators and condensers. However, tubular manifolds are relatively difficult to punch or pierce in order form tube ports. Two-piece manifolds that comprise a tank plate and header plate overcome this problem by locating the tube ports in the header which can be relatively flat to facilitate piercing or punching. The header plate is then mechanically or metallurgically secured to the tank plate to define a passage that fluidically communicates with the tube ports. To increase heat transfer (by improving refrigerant distribution) and the high strength of the manifold, either or both of the tank and header plates can be formed to have multiple channels such that the resulting two-piece manifold has multiple parallel internal passages extending the length of the manifold.
The end of a tube can restrict flow through a manifold if the tube is installed too far into its tube port, and may block flow entirely if the end contacts the tank plate. For this reason, either the tank plate or the tubes are typically formed to define tube stops that positively locate the ends the tubes within the manifold. An example is disclosed in commonly-assigned U.S. Pat. No. 6,155,340 to Folkedal et al., which makes use of a one-piece extruded manifold in which multiple parallel passages are defined. Each passage has a substantially circular shape and is separated from adjacent passages by walls, which also extend along the length of the manifold. Tube ports are formed by machining holes through one surface of the manifold and partially through the walls that separate the passages. The portions of the walls that remain serve as integral tube stops, limiting the extent to which the tubes can be inserted into the manifold so as to prevent the tube ends from excessively restricting the flow of heat transfer fluid through the passages. Other types of tube stops formed by raised surface features on the tank plate of a two-piece manifold are also known, as shown U.S. Pat. Nos. 4,971,145 and 5,172,761.
A difficulty encountered with manifolds having integral tube stops is the cost and practicality of production in very large quantities. A heat exchanger, manifold that makes possible a simplified process of forming tube ports and tube stops would be desirable.
The present invention provides a heat exchanger manifold comprising tank and header members secured together to define an interior of the manifold, with openings formed in the header member to receive heat exchanger tubes, and with tube stops for the tubes defined by raised surface features on the interior surface of the header member, as opposed to the tank member.
The tank and header members of this invention have interior surfaces that face each other and the interior of the manifold. The header member comprises a base portion and at least one raised surface feature rising therefrom that define the interior surface of the header member. The feature is oriented parallel to the longitudinal length of the manifold so as to define at least two longitudinal channels in the interior surface of the member. When the tank and header members are assembled, the surface feature of the header member preferably contacts the interior surface the tank member, so that the channels in the header member define longitudinal passages within the interior of the manifold. One or more openings extend through the base portion of the header member and through at least a portion of the surface feature. The openings are sized to receive tubes with ends having complementary shapes to that of the openings.
According to the invention, the extent to which a tube received in one of the openings can extend into the interior of the manifold is determined at least in part by the width of the opening through the surface feature. This portion of the opening defines what is termed herein a transverse gap that separates opposing portions of the surface feature defined by the opening. If the transverse gap in the surface feature has a width that is less than the width of the remainder of the opening through the base portion, at least one of the opposing portions of the surface feature will be present in the opening, creating a step in the size of the opening. A tube fully inserted into such an opening will abut the portion (step) and thus be prevented from contacting the interior surface of the tank member. As a result, there exists a standoff gap between the end of the tube and the interior surface of the tank member through which a heat transfer fluid is able flow between the end of the tube and the passages within the manifold. Furthermore, the transverse gap formed by the opening through the surface feature allows the heat transfer fluid to flow between the end of the tube and each of the manifold passages. On the other hand, if the opening has a uniform width through the header member and its surface feature, i.e., the width of the transverse gap is the same as the width of the opening, a tube can be inserted into the opening without encountering a tube stop. In this case, the tube can be inserted until it abuts the interior surface of the tank member, with the result that the end of the tube defines a baffle that may restrict or divert flow through the manifold.
From the above, it can be appreciated that as long as a portion of the raised surface feature remains in the opening in the header member, a step is present that provides a tube stop for a tube inserted into the opening. The width of the opening through the raised surface feature and the distance of the step from the interior surface of the tank member determine the widths of the transverse and standoff gaps, respectively. Flow distribution of the heat transfer fluid within the manifold can be altered by varying the widths of these gaps to promote flow through any one of the passages. For example, the width of the transverse gap through the surface feature can be tailored to promote flow toward either of the manifold passages. In this manner, flow can be promoted to the front and then the back of the heat exchanger in alternate tubes, thereby optimizing flow through the heat exchanger. If the tubes are microtubes that are brazed in the openings, the stops can also have the beneficial effect of inhibiting the flow of brazing material into the small parallel passages of the microtubes, thereby reducing the risk that the microtube passages will become plugged by the brazing material.
From the above, it can also be seen that the manifold of this invention can make use of an uncomplicated die and punching operation to simultaneously produce the openings in the header member and tube stops for tubes inserted in the openings. A significant aspect of the invention is the ability to produce the header member by extrusion, taking advantage of the two-dimensional aspects of extrusion technology to mass produce a header member that largely defines the manifold passages and provides the structural integrity of the manifold. As a result, the tank member can have an uncomplicated plate-shaped configuration that can be formed by stamping or any other suitable process. Optionally, the tank member can be fabricated to have one or more raised surface features located and sized to block one or more of the channels in the header member, thereby defining baffles within the longitudinal passages of the manifold. The raised surface features can formed in the tank member to provide any number of baffles that can be to alter the refrigerant flow and distribution within the manifold.
Other objects and advantages of this invention will be better appreciated from the following detailed description.